1. Field of the Invention
The present embodiments relate to a thin film transistor, and more particularly, to a thin film transistor having an oxide layer and an organic light emitting display device having the same.
2. Description of the Related Art
An active matrix flat display device such as a liquid crystal display device or an organic light emitting display device includes at least one thin film transistor (TFT) in each pixel.
The thin film transistor includes an active layer providing a channel region, a source region, and a drain region, and a gate electrode formed in an upper side of the channel region and electrically insulated from the active layer by a gate insulating layer.
The active layer of the TFT is generally formed into a semiconductor layer such as amorphous silicon or poly-silicon.
When the active layer is made of amorphous silicon, mobility is low so that it is difficult to implement a driving circuit operated at high speed.
When the active layer is made of poly-silicon, the mobility is high but its polycrystalline nature causes threshold voltage not to be uniform.
Meanwhile, when low temperature poly-silicon (LTPS) is used as an active layer, the active layer exhibits high mobility and stable DC stability. However, it is difficult to implement a large scale TFT and an additional expensive crystallizer is required which causes manufacturing costs to increase.
In order to solve the above-mentioned problems, recent research for using oxide semiconductors such as ZnO and InGaZnO as an active layer have been carried out. However, these oxide semiconductors have higher mobility than amorphous silicon and better uniformity than low temperature poly-silicon but have drawbacks in terms of mass production.
Some oxide semiconductors have unstable DC stability in connection with reliability of a TFT device so that threshold voltage continuously moves during the operations and it is difficult to implement desired characteristics of the device.